(a) Field of the Invention
The present invention pertains to alloys used as the material for galvanic protectors intended for employment in electrochemical corrosion protection of various articles, structures and constructions manufactured from iron and steel and employed in various aqueous environments, including underground environments.
(b) Description of the Prior Art
For example, there are known magnesium base alloys used as galvanic protectors and consisting essentially of 90 and more weight percent magnesium, the balance being zinc and aluminum (cf. Physico-Chemical Mechanics of Materials, 1973, No 6, pp. 76-79).
The above-mentioned alloys used as galvanic protectors are disadvantageous in that they are characterized by a low electrical output (about 1000 A.h/kg, which amounts to 50-60 percent of theoretical electrical output), and fails to afford effective corrosion protection to iron and steel due to the formation of oxide film on their surfaces, this resulting in passivation of the alloys as well as in lower potential of the protection current.
The prior art also teaches an aluminum base sacrificial anode, comprising 0.005 to 0.03 weight percent gallium (cf. Boshoku Gujutsu, 1974, No 4, pp. 191-195).
The aforementioned alloy sacrificial anode is effective when used in waters high in salts, for example, in seawater, and fails to ensure protection to iron and steel structures brought in contact with drinking water and soil water low in salts (up to 10 mg/l).
U.S. Pat. No. 3,878,081 discloses an aluminum sacrificial anode consisting essentially of 0.02 to about 2 weight percent bismuth, about 0.005 to 0.05 weight percent gallium, about 0.005 to about 0.5 weight percent indium, the balance being essentially aluminum.
The aluminum alloy sacrificial anode of the patent referred to above has insufficiently good electrochemical properties (a current density in a fresh water electrolyte with a resistivity of 5,000 ohm.cm is 10 ma/ft.sup.2, and 50 ma/ft.sup.2 in a saturated calcium sulfate electrolyte). In addition, the aluminum alloy composition includes difficulty available and expensive metals, such as indium, bismuth.